Handle smart contract transaction express nodejs

Question

I have been coding my small project but I'm facing a problem. here is my code:

app.get('/thu', (req, res) => {
  thu(function(err, output){
    if(err){
      res.json({"err": ""+err, "output": output});
      return;
    }
    res.send("ket qua: ", output);
  });
});
var thu = function(callback){
  web3.eth.getTransactionCount(senderAddress).then((txnCount) => {
    console.log("goi thu");
    var method = contract.methods.thu();
    var encodedABI = method.encodeABI();
    var thuTx = {
      from: senderAddress,
      to: contractAddress,
      nonce: web3.utils.toHex(txnCount),
      gasLimit: web3.utils.toHex(GAS_LIMIT),
      gasPrice: web3.utils.toHex(GAS_PRICE),
      data: encodedABI,
    };
    sendTxn(thuTx, callback);
  }).catch((err) => {
    console.log("web3 err", err);
    callback(err, null);
  });
};

function sendTxn(rawTx, callback) {
  var privateKeyBuffer = new Buffer(privateKey, 'hex');
  var transaction = new tx(rawTx);
  transaction.sign(privateKeyBuffer);
  var serializedTx = transaction.serialize().toString('hex');
  web3.eth.sendSignedTransaction(
  '0x' + serializedTx, function(err, txnHash) {
    if(err) {
      console.log("txn err", err);
      callback(err, null);
    } else {
      console.log("txn result", txnHash);
    }
  }).catch((err) => {
    callback(err, null);
  });
}

I'm sure that my smart contract runs ok. when I hit submit the code send a transaction to Rinkeby and it is ok. but I cannot receive any responses. Please help my solve my problems. thank you.

Answer 1

sendSignedTransaction returns a Promise combined event emitter.

Ethereum as a blockchain has different levels of finality and therefore needs to return multiple “stages” of an action. To cope with requirement we return a “promiEvent” for functions like web3.eth.sendTransaction or contract methods. This “promiEvent” is a promise combined with an event emitter to allow acting on different stages of action on the blockchain, like a transaction.

You can place a console.log on every event, to see what is happening, or if you're getting an error.

web3.eth.sendSignedTransaction('0x' + serializedTx)
    .once('transactionHash', hash => console.log(`Hash: ${hash}`)
    .once('receipt', receipt => console.log(`Receipt: ${receipt}`)
    .on('confirmation', (confNumber, receipt) => console.log(confNumber))
    .on('error', error => console.error(error))
    .then(receipt => {
        // will be fired once the receipt its mined
    });

Answer 2

Problems solved. the problem is I forgot the put the callback(...) in else {...}.